1. Field of the Invention
The present invention generally relates to time division multiplex (TDM) data transmission systems, and more particularly to a device and method for selectively obtaining access to individual channels of a TDM bit stream without de-multiplexing thereof, principally to allow testing of such channels.
2. Description of the Prior Art
In the operation of digital transmission systems, it is the practice to multiplex large numbers of subscriber data channels into one high-speed digital bit stream and to transmit the bit stream over various transmission media such as cable and radio. Normally, the bit stream may pass through central offices, relay terminals, and transmission equipment without de-multiplex of the bit stream being necessary. However, to assure the proper operation of the subscriber end equipment and transmission paths, it is necessary to selectively monitor and periodically test subscriber equipment from central offices.
Prior art subscriber channel testing has been limited to points at which physical access to the individual subscriber lines is possible. In this practice demultiplex equipment is necessary, manual connections of test equipment to each line to be tested is required, and time-consuming research of network and routing records is required to determine the location of the access points.